in surgery, a tube made of different metals, principally of silver and lead, but sometimes of iron.

They are introduced into hollow ulcers, in order to facilitate a discharge of pus or any other substance; or into wounds, either accidental or artificial, of the large cavities, as the thorax or abdomen: they are used in the operation of bronchotomy; and, by some, after cutting for the stone, as a drain for urine.

Other cannulas are used for introducing cauteries, either actual or potential, into hollow parts, in order to guard the parts adjacent to that to be cauterized,